1. Field of the Invention
In the context of the present disclosure, a hearing aid should be understood as a small, microelectronic device designed to be worn behind or in a human ear of a hearing-impaired user. A hearing aid system may be monaural and comprise only one hearing aid or be binaural and comprise two hearing aids. Prior to use, the hearing aid is adjusted by a hearing aid fitter according to a prescription. The prescription is based on a hearing test, resulting in a so-called audiogram, of the performance of the hearing-impaired user's unaided hearing. The prescription is developed to reach a setting where the hearing aid will alleviate a hearing loss by amplifying sound at frequencies in those parts of the audible frequency range where the user suffers a hearing deficit. A hearing aid comprises one or more microphones, a microelectronic circuit comprising a signal processor, and an acoustic output transducer (which may also be denoted a hearing aid receiver). The signal processor is preferably a digital signal processor. The hearing aid is enclosed in a casing suitable for fitting behind or in a human ear.
The mechanical design has developed into a number of general categories. As the name suggests, Behind-The-Ear (BTE) hearing aids are worn behind the ear. To be more precise, an electronics unit comprising a housing containing the major electronics parts thereof is worn behind the ear. An earpiece for emitting sound to the hearing aid user is worn in the ear, e.g. in the concha or the ear canal. In a traditional BTE hearing aid, a sound tube is used to convey sound from the output transducer, which in hearing aid terminology is normally referred to as the receiver, located in the housing of the electronics unit and to the ear canal. In some modern types of hearing aids a conducting member comprising electrical conductors conveys an electric signal from the housing and to a receiver placed in the earpiece in the ear. Such hearing aids are commonly referred to as Receiver-In-The-Ear (RITE) hearing aids. In a specific type of RITE hearing aids the receiver is placed inside the ear canal. This category is sometimes referred to as Receiver-In-Canal (RIC) hearing aids.
In-The-Ear (ITE) hearing aids are designed for arrangement in the ear, normally in the funnel-shaped outer part of the ear canal. In a specific type of ITE hearing aids the hearing aid is placed substantially inside the ear canal. This category is sometimes referred to as Completely-In-Canal (CIC) hearing aids. This type of hearing aid requires an especially compact design in order to allow it to be arranged in the ear canal, while accommodating the components necessary for operation of the hearing aid.
In the present context the real ear response is to be interpreted as the determination of the sound pressure provided by a receiver in an earpiece, at a given excitation, to the eardrum of a user, when the earpiece is inserted in the ear canal of the user.
The excitation of the receiver is typically a driving voltage but may also be e.g. a driving current. The earpiece is typically a part of a hearing aid, but may also be e.g. part of an independent device for determination of the real ear response.
Individual variations in ear canal geometry, eardrum impedance and earpiece insertion causes significant variations in the response of a hearing aid receiver when mounted on real, individual ears. A variation across ears of 10 dB (or even more) is not uncommon.
In order to obtain a precise fitting of the hearing aid it is therefore necessary to measure and account for the real ear response on the individual real ear.
2. The Prior Art
It is well known within the art of hearing aids to measure the real ear response by inserting a thin probe microphone tube along with the earpiece to pick up the sound pressure as close as possible to the eardrum. Due to reflection of the sound waves by the eardrum the sound pressure at the eardrum and at other positions in the ear canal may differ. The probe microphone tube must therefore be inserted carefully and fixed to stay near the eardrum while also having the earpiece inserted in the ear canal. This is a time consuming procedure and not very comfortable for the hearing aid user. In some countries this task may only be performed by specifically qualified personnel.
Furthermore the tube may introduce a leakage between the earpiece and the ear canal wall causing an unrealistic venting and so bias the assessment of the real ear response, especially at low frequencies.
It has also been suggested within the art of hearing aids to determine the real ear response based on the sound pressure measured at other positions than right at the eardrum, typically by having a probe tube microphone extending from the earpiece into the residual volume so that the sound pressure is measured a distance, say 5 mm, from the surface of the earpiece. However, such a microphone will not be exposed to the same sound pressure as the eardrum, and the suggested methods all require complicated and careful calibration, high accuracy measurements and complex post processing, making them less suitable for routine clinical use.
For a measurement of the real ear response as part of the fitting procedure it would be convenient if the measurement would not involve handling and insertion of probe tubes and would not require extra steps to be carried out by the hearing aid fitter. For real ear response measurements to become a generally accepted part of the hearing aid fitting procedure this is very important.
It is therefore a feature of the present invention to provide a method of fitting a hearing aid system with improved precision.
It is another feature of the present invention to provide a method of fitting a hearing aid with improved precision and comprising the step of measuring the real ear response without requiring the hearing aid fitter to use probe tubes or to carry out additional measurements.
It is yet another feature of the present invention to provide a hearing aid adapted to provide a hearing aid fitting with improved precision.